A major problem affecting pulp and paper industry worldwide is the increasing cost of suitable wood fiber. Consequently, the tissue industry is always searching for alternative low-cost fiber species for sustainable manufacturing. Also environmental groups and consumers who prefer to use green products have advocated for the use of non-wood fibers as being more environmentally friendly than wood fibers. In order to reduce the reliance on commodity wood pulp, the use of recycled fibers can be a partial solution, but the use of recycled fibers in tissue products is technically limited by the end product quality acceptable to users.
As an alternative, certain non-wood fibers, such as field crop fibers or agricultural residues, are considered as being more sustainable. Examples includes kenaf, flax, bamboo, cotton, jute, hemp, sisal, bagasse, corn stover, rice straw, wheat straw, hersperaloe, switchgrass, and the like. Non-wood fibers are believed to account for about 5 to 10 percent of global pulp production, but are limited for a variety of reasons, including seasonal availability, problems with chemical recovery, brightness of the pulp, silica content, etc. In addition, all land based plants still contain substantial quantities of lignin. Significant energy and chemical input is required to remove lignin in order to get fibers suitable for most paper making.
As a further alternative, algae biomass has been proposed as an alternative fiber source and has several advantages. In particular, algae biomass has no lignin and is known to grow faster and provide a higher yield in comparison to fibers harvested from trees. Similarly to trees, algae are efficient in utilizing carbon dioxide in order to abate air pollution and global warming. Algae are also increasingly being used to reduce excessive nutrients in water due to uncontrolled releases of pollutants from industry and human activities. In addition, algae cultivation does not compete for land usage. Over the years, different kinds of algae have been adapted for a variety of industrial applications. For instance, adsorbent materials comprising microalgae, such as Chlorella or Spirulina, are adapted to remove toxins and odor in cigarette smoke and air, or using brown algae to remove heavy metals from wastewater with absorbent particle sizes varied from 500 μm˜2 mm. Others have used the microalgae Chlorella, in combination with a consortium of prokaryptic microorganisms, to effectively purify wastewater effluent streams using a photobioreactor. Researchers have developed methods to identify algae species and compositions that are effective for lipid production, wastewater and air remediation, or biomass production.
Recent work in adapting microalgae for industrial uses have concentrated on their refinement as biofuels, which is an outgrowth of increasingly limited fossil fuel resources and relative high cost of petroleum. Biomeal, a leftover waste material from the microalgae to biofuel processing, is normally used for animal feeds. (See, e.g., U.S. Pat. No. 6,338,866 and International Patent Publication No. WO 01/60166 to Criggall et al., which developed methods to manufacture pet or animal foods using such a waste product which includes the cell carcasses that remain after one or more essential fatty acids such as docosahexaenoic acid (DHA) have been extracted from lysed algae cells such as Crypthecodinium cohnii; WO Publication No. 2008/039911 to Lo et al. provides a method of optimizing pet food palatable components comprising algal biomeal.)
In many cases, biomeal from microalgae biomass processing is treated as a waste and disposed of in landfills or compost piles. Therefore, a value-added utilization of the microalgae biomass will be a very attractive approach. Activities in microalgae production and utilization will increase in the future because there is a need to reduce global warming and clean up wastewater effluent. On the other hand, petroleum-based oil products that predominate in the energy market today are not sustainable. As a result, it is expected that there is a large amount of microalgae to be used for biofuel refining processes described in U.S. Patent Application Publication Nos. 2008/0155888 to Vick et al. and 2008/0090284 to Hazlebeck et al. Biomeal or a leftover material from microalgae to biofuel refining processes will be abundantly available because the estimated microalgal meal as a byproduct is 0.77 pound for every pound of microalgae processed for oil. Therefore, effective utilization of such a waste material for use in tissue products manufacturing becomes important to any business that is currently depending on petroleum as a feedstock.
Microalgae are generally very small. The small size causes difficulties and limits in the amount of microalgae that can be maintained within the fiber sheet, particularly in low basis weight paper products such as tissue. Small size and lack of significant amounts of cellulosic material may also result in lower strength. Accordingly, there exists a need for methods for increasing the microalgae retention of fiber sheets. Therefore, there is a need to provide a way to effectively utilize algae biomass in the manufacture of tissue products, such as facial tissue, bath tissue and paper towels.